Performance of a digital subscriber line (DSL) in terms of capacity depends on a number of factors such as attenuation and a noise environment. Performance of a DSL transmission system is impacted by crosstalk interference from one twisted line pair to another twisted line pair with the same binder and, to a lesser extent, twisted line pairs in neighboring binders.
Consequently, crosstalk interference may affect data rates across a number of twisted pair lines.
For instance two communication lines such as two very-high-bitrate digital subscriber line (VDSL2) lines which are collocated next to each other induce a signal in each other. Due to the induced crosstalk and noise from other sources in the surroundings of the communication line, the data transported on these lines may be affected or corrupted by the crosstalk and noise. By reducing the crosstalk induced on a communication line or compensating the crosstalk induced on a communication line, the amount of corrupted data may be reduced and the rate at which information can be reliably communicated is increased.
Existing solutions for reducing crosstalk and noise include utilizing a pre-coding control mechanism, which has an optimal performance for crosstalk channel matrices that are diagonally dominant.
Pre-coding (also referred to as pre-compensation) techniques are based on transmitting an additional signal added to the data signal which is used to compensate for the crosstalk on a victim line from external sources. Thus, instead of reducing the effect of crosstalk or avoiding crosstalk effects by configuring the communication line in an appropriate way, pre-coding can be used to compensate for the effects of crosstalk on a communication channel. Pre-coding techniques are based on crosstalk channel information that includes both amplitude and phase information. Such information can be obtained from measurements such as slicer error or signal-to-noise ratio (SNR). A particular example of such measurements for pre-coding is the use of pilot sequences and error feedback. The use of pilot sequences in G.vector is described in “Self-FEXT cancellation (vectoring) for use with VDSL2 transceivers,” Series G: Transmission Systems and Media, Digital Systems and Networks, ITU G.993.5, April 2010, the entire contents of which is incorporated by reference.
A crosstalk channel matrix may refer to a matrix that indicates levels of noise and crosstalk interference induced by each active communication line on other active communication lines (in the case of the two communication lines discussed above, the corresponding crosstalk matrix is a 2 by 2 matrix).
A diagonally dominant matrix is a matrix in which a magnitude of a diagonal entry in each row of the matrix is greater than or equal to a sum of the magnitudes of all other entries in the same row of that matrix.